Computer networks allow users to access information stored within, or associated with, the network. A typical computer network can include multiple client computers that communicate with each other through a system of data communications devices (e.g., switches and routers) and transmission media (e.g., electrical wiring, fiber-optic cable, and/or wireless connections). In general, a transmitting client device exchanges data with a receiving client device by packaging the data using a standard format or protocol to form one or more data structures (e.g., packets, frames, or cells). The transmitting client device transfers these data structures to the receiving client device through the above-described system of computerized devices and transmission media. Once received, the receiving client device can unpackage the data structures and use the data.
Conventional computer networks can be subject to unwanted intrusion or attacks. For example, devices on a network can be subject to user-level network attacks, such as drive-by-downloads (e.g., computer virus or malware) that can occur without a user's knowledge, such as when the user visits a particular website. Network devices can also be subject to user-level network attacks, such as phishing attacks, which can obtain relatively sensitive information, such as passwords and user names from the devices.
To combat user-level network attack, the functionality of intrusion-detection systems (IDS) or tools such as software-defined networking (SDN) can be utilized by computer networks. In software-defined networking, such as provided by the OpenFlow protocol, each network device in the network is configured to review various aspects of network traffic, such as source and destination information. Based upon the review, in the case where the network device is unclear as to how to process the traffic, the network device is configured to request permission from a server device (e.g., a central server device) prior to forwarding the traffic within the network. The server device makes the decision with respect to the traffic.